What Size Trimmer Line Should I Use? Start With Your Trimmer Manual

Use the line diameter printed in your trimmer’s manual, because the motor and the head are built around that size. Battery trimmers list anywhere from 0.065 to 0.095 in, and a line thicker than the manual allows overloads the motor. On my sprayers the nozzle size was fixed by the pump, and trimmer line works the same way: a bigger size only adds load. I trim the strips under my plum and apricot rows and the fence lines around the yard, so line size decides how my afternoons go. Below you get the sizes for ten real models, what a wrong size does, how to match the job and how to change line safely.

What Size Trimmer Line Should I Use? The Short Answer

Use the diameter your manual lists and treat the largest size it names as a hard cap. The maker matched the line to the motor and the head, and the manual is where that match is written down. For the battery trimmers in the table below the sizes run from 0.065 in to 0.095 in.

The reason is load. According to Craftsman, heavier gauge line on its V20 trimmer “will overload the motor and cause overheating.” EGO lists heavy line among the causes of a head that will not advance line and of a trimmer that stops while cutting. A bigger number on the spool never means a better setup.

Eyes take the worst of it. In US emergency department data from 2000 to 2009, the eye accounted for 42.5 percent of an estimated 81,907 lawn trimmer injuries (1). EGO says a battery trimmer is always in operating condition until the pack is out, so the order is always the same: switch off, wait for the head to stop, then take the pack out.

Trimmer Line Size Chart by Model

This trimmer line size chart lists what the manuals say for ten popular models. Read the last column first, because the cap is the number that protects the motor.

Models That List Two Sizes

The Echo, DeWalt, Milwaukee and EGO ST1502SA entries name two sizes. In that case the larger size is the cap. Where the manual recommends one of the two, as EGO does with 0.095 in, use the recommended one. Where it names no favorite, I start with the smaller size and never go past the cap.

Stihl and Gas Machines

For Stihl trimmer line size, the maker sells round line from 0.065 to 0.130 in, and it also says not all diameters are approved for all of its trimmers. Your model’s manual decides. Gas machines can take more: Husqvarna’s manual for one 41.5 cc brush cutter lists heads that take cord from 2.4 mm up to 3.0 mm, about 0.095 to 0.118 in.

What Line Size Does to the Motor

The spinning line is the load the motor works against. Everything below follows from that one fact. My guide to how a string trimmer works shows how the head, the line and the drive fit together.

Why Oversized Line Overloads the Motor

EGO tells the user to “allow the very tip of the line to do the cutting” and says cutting with more than the tip “may overload the motor.” Line above the cap makes the same tip heavier and harder to push through growth. The motor answers with heat, and the battery answers with a short run.

That is why the cap exists. It is also why a trimmer that stops mid-row on a hot afternoon deserves a check of the line before anything else.

How Far the Line Should Reach

The maker’s cutting swath is the circle the line draws at its proper length, and the small blade on the guard trims the line to that length. DeWalt says line past its 15 in swath harms performance, runtime and motor life. Craftsman says the same for its 13 in swath on the CMCST920. Echo warns that without its cut-off knife the line grows too long, “the engine will overheat” and damage may follow. I match swath to yard size in a separate guide to the string trimmer cutting width that fits each lawn.

Length also changes how the tool feels. In a test on one gas grass trimmer, nylon thread length, engine speed and handle material all changed hand-arm vibration, and the lowest reading came with a 100 mm thread (2). That result belongs to one machine and says nothing about diameter, but it shows why I let the guard blade do its job and never pull extra line out by hand.

A Worked Example With Real Numbers

The Milwaukee 2825-21ST manual lets you load 25 ft of 0.080 in line or 20 ft of 0.095 in line. The thicker line gives 5 ft less on the same spool, which is 20 percent less line per reload.

The DeWalt DCST970 takes up to 25 ft with 5 in left on each side, and the EGO ST1502SA calls for a 16 ft piece. Each model has its own load, so read the figure in your manual before you cut the line. I go through that kit in my review of the DeWalt DCST970, including its FLEXVOLT pack and 15 inch swath.

I plan reloads for the end of a row, never the middle, and I carry a pre-cut length so the stop takes minutes.

Match the Line to the Job Inside Your Range

Within the range your manual allows, the job decides where you sit. The cap never moves.

Lawn Edges and Tree Rows

Along the strips under my trees I use the smaller size the manual lists. EGO warns that tree bark, siding and fence posts “can easily be damaged by the strings,” and my trees were planted in 2016, so the bark at the base is still thin. I keep the head off the trunk and run the tip along the grass edge instead.

The drip lines lie on the soil near the same strips. I lift or mark them before I trim, because spinning line cuts plastic as easily as grass.

Fence Lines and Gravel Edges

EGO notes that wire and picket fences cause extra string wear or breakage, and that stone, brick and curbs wear line quickly. Along my fence lines and the gravel yard I expect to reload more often, and I wear eye protection every minute because stones fly. A bystander can be hurt as well: case reports describe injuries to people standing near a line trimmer (3). The EGO ST1502SA manual and the DeWalt DCST970 manual both ask for 100 feet between the tool and other people or pets, and I follow the distance in the manual for the tool in my hands.

If thick weeds are the problem, the answer is to cut from the top down in small passes, as EGO advises for grass over 8 in. The answer is never a heavier line than the manual allows. For stands that really are dense, my list of trimmers for thick weeds sorts the battery and gas options that cope.

Check the Cap Before You Buy

When the fence line is your main job, look up the maximum approved line diameter in the manual before you pay, because the string trimmer line size your manual approves for the exact tool and head sets that limit, and the spec page may list only one of them. A trimmer capped at 0.065 in, like the Black+Decker LST136 or the Greenworks 40V 2101602, has no room to go up.

Shape, Brand and Material of Trimmer Line

Diameter is the number that matters most, but the manuals also name a shape and a source. Here is what they say.

Shape Is a Fit Question

The manuals name the shape their head takes. Black+Decker and Craftsman name round line, DeWalt and Milwaukee name spiral line with smooth round edges, and EGO names twist line. Craftsman adds a ban on serrated line for its CMCST900. The makers do not rank round against twisted, square or serrated line, so I pick the shape my manual names and move on. Heads also differ in how they feed that line, and my automatic feed string trimmer guide compares automatic and bump feed.

Same-Maker Line and What Never to Use

DeWalt and Craftsman say another maker’s line “can reduce performance, damage the trimmer or cause personal injury.” Stihl says its Premium Round line is made to fit its own and competing heads, and the same page says not all diameters suit all Stihl trimmers. Both statements lead to the same step: match the diameter to the manual first.

Never use metal-reinforced line, wire, cable, rope or fishing line. EGO says such material “can break off and become dangerous projectiles.”

How to Find and Load the Right Size Safely

The manuals agree on the safety order. The loading steps differ by head, so follow your own manual for those.

1. Switch the trimmer off and wait until the head has stopped. Then remove the battery. On a gas trimmer take off the spark plug wire, and on a corded one unplug it.
2. Open the manual to the specifications page and find the line diameter. When it lists two sizes, the larger one is the cap.
3. Find the load length. It is 16 ft on the EGO ST1502SA, up to 25 ft on the DeWalt DCST970 and 20 ft pieces on the Echo PAS-225VP.
4. Load the head the way your manual shows. On the EGO ST1502SA, the DeWalt DCST970 and the Echo PAS-225VP one piece goes through the eyelets until equal lengths show on each side. The Greenworks 40V 2101602 takes two pieces of about 10 ft, each wound into its own anchor hole, and the EGO ST1623T, which I cover in my review of the EGO ST1623T, winds its line by motor with the POWERLOAD button. For that powered step the ST1623T manual has you thread the line with the battery out, then install the battery before you press POWERLOAD, so switch off, wait for the head to stop and take the battery out again before you touch the head.
5. Keep the guard on so its blade can trim the ends to the proper length.
6. Put the battery back only when the manual’s steps are done (for the ST1623T, it goes in before the POWERLOAD winding), and keep bystanders at the distance the manual gives.

Gear matters on long jobs too. In one lab study a gloved hand on a grass trimmer saw 3.5 to 5.8 m/s2 of vibration, against 1.1 to 2.0 on a backpack blower, and gloves reduced it (4). In NIOSH sampling of landscaping workers, 94 of 119 shift noise results were at or above the 85 dBA limit, and fuel-powered trimmers added more noise and carbon monoxide than battery versions (5). My battery versus gas string trimmer guide helps you choose between those power types for your yard.

Mistakes I See With Trimmer Line

These errors come back every season. The size rules above cover the cap, the swath and mixing makers, so this list holds the handling mistakes.

• Overfilling the spool: one gas trimmer manual warns that line may jam if more than 18 ft is loaded, so cut the length the manual gives.
• Bumping an automatic head: the Black+Decker LST136 manual says not to bump the head, because it disrupts the feed. I cover the 40V MAX trimmer and edger kit in my Black+Decker LST136 review.
• Unequal ends: on heads loaded with one piece through two eyelets, the manuals call for equal lengths on both sides.
• Skipping the shutdown order: switch off, wait for the head to stop, then remove the battery, take off the spark plug wire or unplug, and only then touch the line.

Pick the Size Your Trimmer Was Built For

Read the diameter in the manual and treat the larger size as the cap. Then let the guard blade set the length and stay with the line your manual names. My own habit is to keep the spare spool with its tape label beside the charger.

Open your manual at the specifications page tonight and write down the line size and load length. The right size of trimmer line is the one your maker printed for your motor and head. Once the line is settled, my guide to the string trimmer size you need helps with the machine itself.

Frequently Asked Questions

Which is better, .080 or .095 trimmer line?

Neither .080 nor .095 trimmer line is better on every trimmer, because the better size is the one your manual lists. The EGO ST1623T takes 0.095 in only, while the Milwaukee 2825-21ST and the DeWalt DCST970 accept both. When a manual lists two sizes, the larger one is the cap.

Is it better to have thicker or thinner trimmer lines?

Thicker or thinner trimmer line is only better inside the range your manual allows. Past the larger size the motor overloads and overheats, and a trimmer capped at 0.065 in, such as the Black+Decker LST136, takes nothing thicker.

What happens if you use the wrong size trimmer line?

A line thicker than the manual allows overloads the motor and can cause overheating, according to Craftsman, and EGO lists heavy line among the reasons a trimmer stops or a head will not advance line. DeWalt and Craftsman add that another maker’s line can reduce performance or damage the trimmer.

Is .105 or .095 trimmer line better?

.095 trimmer line is better than .105 on the models whose manuals cap the size at 0.095 in, such as the EGO ST1623T. .105 line fits only heads that list it, and some gas heads do. Check the head’s size range in the manual before you buy.

Does trimmer line size matter?

Trimmer line size matters because the maker sets the diameter range for the motor and the head. A line thicker than that range overloads the motor, and Milwaukee says any other size can degrade performance or cause damage.

References

1. Leinert J, Griffin R, Blackburn J, McGwin G. The epidemiology of lawn trimmer injuries in the United States: 2000-2009. J Safety Res. 2012;43(2):137-139. doi:10.1016/j.jsr.2012.03.001
2. Mallick Z. Optimization of the operating parameters of a grass trimming machine. Appl Ergon. 2010;41(2):260-265. doi:10.1016/j.apergo.2009.07.010
3. Lubniewski AJ, Olk RJ, Grand MG. Ocular dangers in the garden. A new menace: nylon line lawn trimmers. Ophthalmology. 1988;95(7):906-910. doi:10.1016/s0161-6420(88)33076-9
4. Oh J, Chen N, Boyd C. Laboratory evaluation of occupational exposure to hand-arm vibration (HAV) during grounds maintenance equipment operations. Ann Agric Environ Med. 2023;30(2):384-389.
5. Alexander BM, Graydon PS, Pena M, Feng HA, Beamer BR. Hazardous exposures and engineering controls in the landscaping services industry. Journal of Occupational and Environmental Hygiene. 2025;22(3):189-202.

Safety Note: Read your manual first. A string trimmer or brush cutter throws debris with force, so clear stones, glass and wire from the area before you cut. Wear impact-rated eye protection with side coverage that meets ANSI Z87.1, hearing protection, gloves, heavy long pants, long sleeves and sturdy slip-resistant boots (steel-toe where your manual says so). Keep people and pets at least as far away as your manual says (50 feet in some manuals, 100 feet in others), and stop if anyone comes closer. Keep the correct guard fitted, use only the cutting attachments, handles and harness the maker approves for your exact tool, and never replace trimmer line with wire. A blade can kick sideways when it hits a stump or a thick stem, so fit the handlebar and harness your manual requires for blade work, hold both handles firmly and keep secure footing. Before you clear a jam, clean the tool or change line, a blade or an attachment, switch it off, wait for all movement to stop, then remove the battery, unplug the cord or disconnect the spark plug wire. Refuel a gas model outdoors with the engine off and cool, away from flames or sparks, and move away from the fueling spot before starting, as far as your manual says (often 10 to 30 feet); never run it in a garage, shed or other closed space. For a battery model, use only the maker’s battery and charger, charge it within the temperature range in your manual and never use a damaged or swollen pack. For a corded model, use a GFCI outlet, keep the cord clear of the cutting line and avoid wet conditions.